An IC tag whose security is improved is disclosed in Japanese Patent Laid-Open Nos. 2003-337928 and 2003-16396. The IC tag disclosed in the former official gazette has a configuration of storing a power through connection with a terminal, generating a one-time password by a CPU in the IC by means of the power, holding the password in a memory, and deleting the held password when the stored power is discharged and the IC tag disclosed in the latter official gazette has a configuration of reading authentication data from the tag twice or more and using a pseudo random value as authentication data.